1. Field of the Invention
The present invention relates to pasty organopolysiloxane compositions, and, more especially, to such compositions which can be readily transferred or circulated by means of pumps, comprising organic peroxide cross-linking agents and which can be conveniently thermoset to form elastomers possessing good mechanical properties.
2. Description of the Prior Art
Pasty organopolysiloxane compositions consisting of diorganopolysiloxane oils, fillers and organic peroxides, and which can be subjected to thermosetting to form elastomers, are described in U.S. Pat. No. 3,791,998. The objective of this patent is to obtain, in a simple manner, good adhesion between the organopolysiloxane elastomers and fabrics which are to be used as insulators for electrical conductors; this objective is achieved by the use of compositions which are sufficiently plastic to penetrate into the mesh of the fabrics. Thus, said patent does not suggest any method for obtaining elastomers possessing good mechanical properties from pasty organopolysiloxane compositions.
Organopolysiloxane compositions which can have a sufficiently low viscosity to be circulated, and then harden to form elastomers, in low-pressure molding devices or apparatus (such as the so-called liquid injection-molding machines), are described in U.S. Pat. No. 4,173,560. Same consist of diorganopolysiloxane oils having, per mol, about 2 vinyl radicals bonded to the silicon atoms, finely divided silicas treated with vinylic amidoorganopolysiloxanes, and, as cross-linking agents, organic peroxides or more complex systems comprising combinations of organohydrogenopolysiloxanes and platinum derivatives.
These compositions harden to form elastomers having proper mechanical properties; however, the treatment of the finely divided silicas entails the use of organopolysiloxane compounds which are not readily available on the silicone market; moreover, the examples in the patent reflect that, in order to pursue this treatment, it is first necessary to dry the finely divided silicas for a prolonged period of time and then to carry out the process in an anhydrous solvent medium.
U.S. Pat. No. 4,173,560 also teaches (column 7, Example 1A and column 8, Example 3) that the usual treatment of the silicas by means of organosilicon compounds which donate (CH.sub.3).sub.3 SiO.sub.0.5 groups, such as hexamethyldisilazane, leads to elastomers possessing mechanical properties which are on the whole inferior (in particular from the point of view of Shore A hardness) to those of the elastomers produced from compositions containing silicas treated with the vinylic amidoorganopolysiloxanes.